In ICD-10, superior mesenteric vein (SMV) thrombosis is classified under K55.0, acute vascular disorders of intestine, which covers mesenteric venous and arterial thrombosis. In the US ICD-10-CM version, K55.0 is split into more specific codes by site and severity, so the final thrombosis ICD 10 code depends on whether the bowel is ischemic or infarcted and which segment is involved. Associated clotting disorders, portal vein extension, and long-term anticoagulant use are coded separately.
This guide covers both sides of the topic: how SMV thrombosis is coded, and what the condition means clinically, from causes and symptoms to diagnosis and treatment.
What Is SMV Thrombosis?
The superior mesenteric vein drains blood from the small intestine, the cecum, and the ascending and much of the transverse colon. It joins the splenic vein behind the pancreas to form the portal vein, which carries blood to the liver.
SMV thrombosis is a blood clot in this vein. When the clot blocks outflow, blood backs up in the bowel wall, causing swelling, reduced arterial inflow, and eventually mesenteric ischemia. If untreated, the affected bowel can die (infarction), which is a surgical emergency. It is a relatively uncommon cause of mesenteric ischemia, but an important one because it often affects younger patients with an underlying clotting tendency.
SMV Thrombosis ICD 10 Coding
Coding should always follow the documentation and the current official code set. The table below summarizes codes commonly relevant to an SMV thrombosis encounter.
| Code | Description | When it applies |
|---|---|---|
| K55.0 (WHO ICD-10) | Acute vascular disorders of intestine | Acute mesenteric venous or arterial thrombosis, embolism, or infarction |
| K55.0- subcodes (ICD-10-CM) | Acute ischemia or infarction, by intestinal segment and extent | Chosen according to whether the bowel is reversibly ischemic or infarcted, and where |
| K55.1 | Chronic vascular disorders of intestine | Chronic mesenteric ischemia |
| I81 | Portal vein thrombosis | When the clot extends into the portal vein |
| D68.51 / D68.52 (ICD-10-CM) | Activated protein C resistance (factor V Leiden) / prothrombin gene mutation | When an inherited thrombophilia is documented |
| Z79.01 (ICD-10-CM) | Long-term (current) use of anticoagulants | Follow-up encounters on ongoing anticoagulation |
Because the SMV and portal vein form one connected system, clots often involve both. Our guide to portal vein thrombosis ICD-10 coding explains how to handle that overlap. The underlying cause, such as cirrhosis, pancreatitis, or cancer, should also be coded when documented.
Causes and Risk Factors
SMV thrombosis follows the logic of Virchow’s triad: slow blood flow, damage to the vessel wall, and a tendency of the blood to clot. Most patients have at least one identifiable risk factor.
Local Abdominal Causes
- Portal hypertension and cirrhosis, which slow flow in the portal system.
- Inflammation such as pancreatitis, diverticulitis, appendicitis, or inflammatory bowel disease.
- Abdominal surgery or trauma, including splenectomy.
- Intra-abdominal cancers, especially pancreatic and liver tumors.
Systemic Clotting Tendencies
- Inherited thrombophilias, including factor V Leiden, prothrombin gene mutation, and deficiencies of protein C, protein S, or antithrombin.
- Myeloproliferative neoplasms, often driven by a JAK2 mutation, which are a classic hidden cause of abdominal vein clots.
- Antiphospholipid syndrome and paroxysmal nocturnal hemoglobinuria.
- Estrogen-containing contraceptives, pregnancy, and cancer elsewhere in the body.
As a hematologist, I look for a systemic cause in every patient without an obvious local trigger. Our article on hypercoagulability covers the full workup. For broader context on clotting, see the blood clotting guide.
Signs, Symptoms and Diagnosis
Symptoms range from vague to dramatic. The classic warning sign is abdominal pain out of proportion to examination findings, often building over days. Nausea, vomiting, diarrhea, bloating, and blood in the stool may follow. Fever, a rigid abdomen, or low blood pressure suggest bowel infarction.
Imaging
Contrast-enhanced CT of the abdomen in the portal venous phase is the key test. It shows the clot as a filling defect in the vein and reveals bowel wall thickening, fluid, or signs of infarction. Doppler ultrasound can assess flow in the portal and mesenteric veins and is useful for follow-up, while MR venography is an alternative in selected patients.
Laboratory Tests
D-dimer is often raised but is not specific. Lactate may rise with bowel ischemia, although a normal value does not exclude it. Once the diagnosis is made, a thrombophilia and myeloproliferative screen, including JAK2 testing, is considered. Timing matters, because some clotting tests are affected by acute thrombosis and by anticoagulant drugs.
Treatment and Management
Anticoagulation
Prompt anticoagulation is the cornerstone of treatment. Patients usually start on heparin, often unfractionated heparin while surgery remains possible, before moving to an oral agent such as warfarin or a direct oral anticoagulant where appropriate. Treatment typically lasts at least three to six months, and it may be continued indefinitely if a permanent risk factor is found.
Surgery and Intervention
If there are signs of peritonitis or bowel infarction, emergency surgery is needed to remove dead bowel. A planned second-look operation is common, because the viability of borderline bowel can be hard to judge at first. In selected patients who worsen despite anticoagulation, interventional radiologists may use catheter-directed thrombolysis or clot removal.
Follow-Up
Repeat imaging checks whether the vein has reopened. Long-term complications can include portal hypertension, varices, and, after extensive resection, short bowel syndrome.
When to See a Doctor
Seek emergency care for severe or worsening abdominal pain, especially if you have a known clotting disorder, liver disease, recent abdominal surgery, or a previous clot. Blood in the stool, persistent vomiting, or fever with abdominal pain also need urgent assessment. Early treatment gives the best chance of saving the bowel.
Frequently Asked Questions
What is the ICD-10 code for superior mesenteric vein thrombosis?
In WHO ICD-10 it falls under K55.0, acute vascular disorders of intestine. In ICD-10-CM, the K55.0 category has more specific subcodes by segment and severity, so the exact code depends on the clinical documentation.
Is SMV thrombosis the same as portal vein thrombosis?
No, but they are closely related. The SMV feeds into the portal vein, so clots commonly extend from one to the other, and each site is coded separately when both are involved.
How long do people need blood thinners after SMV thrombosis?
Usually at least three to six months. If the clot was linked to a lasting risk factor, such as an inherited thrombophilia or a myeloproliferative neoplasm, longer or lifelong treatment is often recommended.
Can SMV thrombosis be found by chance?
Yes. It is sometimes seen on CT scans done for other reasons, particularly in people with cirrhosis or cancer. Even without symptoms, it deserves specialist review to decide whether treatment is needed.
